ZINC TOLERANCE AND HYPERACCUMULATION IN A NEW ECOTYPE OF SEDUM ALFREDII HANCE

Plants growing on heavy metal polluted soil environment can gradually evolve into differentiated ecotypes. In a survey of plant population in Zn/Pb mining and non mining areas in southeast China,a new Zn hyperaccumulating ecotype of Sedum alfredii Hance was found in an old Zn/Pb mining area. The old mining ecotype showed a thicker stem,larger leaves and greater height and biomass under both natural and controlled growth conditions,relative to the non mining ecotype. Shoot Zn concentration in the old mining ecotype plants which grew on old mining soils with available Zn of 105 5 325 4 mg·kg -1 ,ranged 4134-5000 mg·kg -1 ,and reached as high as 2% under control condition. Shoot Zn concentration of the old mining ecotype plants was over 30 times higher than that of the non mining ecotype plants growing at the same external Zn concentration in the nutrient solution culture experiment (1223 6 μmol·L -1 in nutrient solution for 12 days). The distribution of Zinc in the plant differed between the two ecotypes,being stem leaf roots for the old mining ecotype and root stem leaf for the non mining ecotype. Shoot/root Zn ratio exceeded 10 in the old mining ecotype,but were always 1 for the non mining ecotype. The results showed that the old mining ecotype of S. alfredii Hance is a Zn hyperaccumulating ecotype,which has evolved from long term exposure of plants to a high Zn soil environment. The finding of this ecotype is of importance for understanding micro evolution mechanisms of Zn tolerance and hyperaccumulation of plants,and for providing a new material for phytoremediation of Zn contaminated soils.